Long term research goals involve tailoring treatment to the individual needs of children in foster care. To this end, the specific aims of this proposed research program are to define subgroup distinctions among children who enter the foster care system, develop services appropriate to the specific needs of different subgroups, and assess the effectiveness of the services. Recent advances in neuroscience and developmental psychology will be brought to bear on the assessment of child functioning, with assessments of biobehavioral functioning and of specific behavioral transactions critical to defining subgroups and assessing intervention effects. The proposed program of research attempts to refine our understanding of foster children s specific functioning deficits. Children enter foster care at different ages, and with different caregiving histories; subsequently they have surrogate caregivers who differ in sensitivity. Current research indicates that even for infants, age at placement and sensitivity of the surrogate caregivers matter. Subgroups of children, differentiated roughly by age and caregiver sensitivity, are expected to be identified that have different needs and require different types and dosages of treatment. Services are expected to be most effective if they target the specific functional deficit of a foster parent/child dyad. Therefore, services will be developed and refined that are tailored to the particular needs of these dyads. A pilot project will assess the effectiveness of tailoring services to specifically identified needs of foster infants and their surrogate parents.